Davis's Lab & Diagnostic Tests

Hexosaminidase A and B

Hexosaminidase A and B is a topic covered in the Davis's Lab & Diagnostic Tests.

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TSD (Tay-Sachs disease) testing.

Common Use:
To assist in diagnosing Tay-Sachs disease by identifying a hexosaminidase enzyme deficiency.

Serum collected in a yellow-top (acid-citrate-dextrose [ACD]) or a red-top tube for hexosaminidase enzyme assay; lavender-top (EDTA), pink-top (K2 EDTA) or yellow-top tube (ACD) for molecular polymerase chain reaction (PCR) assay.

Normal Findings:
(Method: Fluorometry for enzyme assay, PCR/primer extension for molecular assay)

Enzyme Assay
Total HexosaminidaseConventional UnitsSI Units (Conventional Units × 0.0167)
Noncarrier589–955 nmol/hr/mL9.83–15.95 units/L
Heterozygote465–675 nmol/hr/mL7.77–11.27 units/L
Tay-Sachs homozygoteGreater than 1,027 nmol/hr/mLGreater than 17.15 units/L
Hexosaminidase AConventional UnitsSI Units (Conventional Units × 0.0167)
Noncarrier456–592 nmol/hr/mL or 55–76% of total hexosaminidase7.62–9.88 units/L or 55–76% of total hexosaminidase
Heterozygote197–323 nmol/hr/mL3.29–5.39 units/L
Tay-Sachs homozygote0 nmol/hr/mL0 units/L
Hexosaminidase BConventional UnitsSI Units (Conventional Units × 0.0167)
Noncarrier12–32 nmol/hr/mL0.2–0.54 units/L
Heterozygote21–81 nmol/hr/mL0.35–1.35 units/L
Tay-Sachs homozygoteGreater than 305 nmol/hr/mLGreater than 5.09 units/L

Molecular assay: Negative for HEXA 7 mutations (samples are evaluated for seven specific HEXA gene mutations).

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